1. Field of the Invention
The present invention relates to a method of manufacturing an optical semiconductor integrated circuit device having a photodiode and intends to eliminate variation of thickness of insulating film laminated on the photodiode and thereby to improve the sensitivity of the photodiode.
2. Description of the Related Art
In a photodiode for blue laser, a transparent package absorbs energy of incident light to cause the burning of the package. Accordingly, for an IC package, a hollow package has to be adopted. As a result, an insulating film on a photodiode formation region is exposed to air in the hollow package. The reflection of incident light at a surface of the insulating film depends on a thickness of the insulating film. That is, a problem is known in that the sensitivity of the photodiode fluctuates as the film thickness of the insulating film fluctuates.
In this connection, as a countermeasure against the fluctuation of the sensitivity due to the fluctuation of the film thickness of the insulating film, there is a technique in which on the photodiode formation region as a surface protective film a single layer of a silicon nitride film is covered (Patent Reference 1).
[Patent Reference 1] JP-A-2001-320078
In the invention according to patent reference 1, the abovementioned silicon nitride film is used, when an insulating film is etched, as an etching stopper film, and, according to wet etching, the insulating film is removed once for all. Accordingly, when the insulating film is removed by etching, since the etching proceeds in a horizontal direction to a surface of the substrate, there are problems in that a desired structure can be obtained with difficulty and the processing accuracy is poor.